Liquid collectors (also known as chimney trays and collector trays) are used in vertical vapor-liquid contact towers designed for countercurrent vapor-liquid flow where the vapor (gas) flows upward and the liquid flows downward. In these towers, various processes require the liquid to be collected and redirected to another section of the tower and/or withdrawn from the tower.
There are generally two types of liquid collector trays that have been developed in the art. The first type uses a sheet-metal floor which occupies the cross-section of the tower at an appropriate location, with round pipe risers or rectangular box risers being used for the upward passage of vapor. The liquid dripping from structures above the tray is collected on the tray's floor and then withdrawn from the side of the tower through, for example, a nozzle. Rather than being withdrawn from the tower, all or some of the liquid may be diverted to another device such as liquid distributor within the same tower immediately below the collector tray. This type of collector tray may be secured in the tower by bolting or welding to a support ring. If a bolted construction is used, an appropriate gasket is employed to make the operation leak tight.
The second type of liquid collector tray employs a series of parallel troughs and thus is known as a “trough-type liquid collector tray.” Trays of this type are also known as “vane type” or “lamella type” trays. The present disclosure is concerned with trays of this type.
FIGS. 8 and 9 are cross-sectional views of a typical trough structure as currently used in the art. Liquid 11 dripping from devices above the tray enters the collector through the space between two adjacent angular lamellae 71 and is collected in the troughs 73 at the bottoms of the lamellae. Vapor 9 rises along the angular sides of the lamellae 71 and finally discharges from the top of the collector.
Compared to the riser-type collector trays, trough-type trays provide substantially greater open areas. For example, a typical collector tray with risers provides an open area equal to 10% to 30% of the cross section area of the tower at the bottom where the vapor enters. For a typical trough-type collector tray, on the other hand, this area can be as much as 60% of the tower cross section area. Therefore, trough-type trays are much more suitable for an atmospheric tower and even more desirable for a vacuum tower as these devices offer lower pressure drops.
Existing trough-type collector trays have, however, suffered from a number of drawbacks. In particular, the trays have had vapor paths, including vapor entrances and vapor exits, that include sharp corners (see FIGS. 8 and 9), which reduce vapor flow and thus lead to additional head losses (pressure drops). Also, the liquid-holding capacity of the trays has been limited by their structure. The present disclosure is directed to trough-type collector trays which address these longstanding deficits in the art.